There are two ways that you can make instant coffee: 1. you can brew the coffee (in large volumes or small ones using ground coffee beans and water) making a very strong coffee solution, that can be likened unto a strong coffee solution. The heating this solution to boil off all the water, one end up with a coffee powder that is actually one form of "instant coffee,"
2. one can make up, a strong coffee solution of coffee and water, as above, in example (1), and instead of boiling off the water, one can subject the coffee solution to a deep vacuum (within a closed container) to cause the water to go from a liquid to a gas (without forming a liquid). This is a "freeze drying" method. One end up with coffee flakes, a form of instance coffee.
The second method required some science background to set up the system, if one is designing the vacuum set up from scratch. However, actually, this is not very difficult science.
My lesson, for making instance coffee, has been quick and simple, but given the great amount of information available on the internet, making one's on instant coffee system can be done. I do not encourage one to do this. It is cheaper to purchase instant coffee, and the quality of the instant coffee that you purchase from a commercial source (or from any supplier, actually) will be superior to any that you will make, to start.